1. Field of the Invention
The present invention relates to an electronic device, and in particular, to a surge absorber.
2. Description of the Related Art
Stray waves, noise, and electrostatic disturbances which may cause surges are strong obstacles to the further improvement of the most up-to-date electronic equipment. Especially, high voltage pulse waves cause erroneous operations of semiconductors in electronic equipment. These waves sometimes even damage semiconductors or the devices themselves.
Such problems can, however, be solved by the use of surge absorbers. Conventional surge absorbers produce discharge chips having an insulating microgap or discharge cores, and the discharge chips are sealed in a glass housing. For example, in a MicroAge surge absorber manufactured by Mitsubishi Materials Corporation, after a conductive thin film is grown in the ceramic core and metal cap electrodes are fitted to both edges of the core, a surface of the conductive thin film is removed by laser and a slit, or MicroAge is formed. Discharge chips (discharge cores) formed in such a manner are sealed in a glass tube. By using such a conventional chip type surge absorber, a discharge voltage can be determined based on a width of the MicroAge mentioned above (a thin groove in the form of slit).
Further, there has been a known surge absorber which is composed of conductive films partitioned by microgrooves. However, as it is difficult to optionally select a switching voltage of such a surge absorber, the range of applications of such surge absorbers is extremely restricted. U.S. Pat. No. 4,727,350 discloses a surge absorber which comprises a cylindrical tube core covered with a conductive film having an intersecting micro groove and the exterior of which is sealed in a glass container.
The applicant of the present invention has also proposed a surge absorber in Japanese Patent Laid-Open Publication No. Hie 8-306467 which solves the conventional problems described above. According to the surge absorber, by arranging a tube core between a pair of electrodes sealed in a housing and filling a surrounding air chamber with an inactive gas, surge absorption can be achieved to a higher switching voltage then was possible in the past.
However, each of the surge absorbers mentioned above has a constitution such that discharge chips or discharge cores (tube cores) are produced in order to determine a discharge curve and the discharge chips or the discharge cores are sealed in a housing. Therefore, the constitution becomes complicated and requires a large number of production processes, and production costs cannot be reduced. Especially, when many surge absorbers must be mounted in an electronic device to protect elements or cope with the fluctuation of power-supply voltage, a number of surge absorbers must be used which directly leads to a problem that the equipment cost of the complete device rises.
Further, according to surge absorbers proposed heretofore, a discharge current flows via a tube core, whereby it is difficult to cope with a high switching voltage of ten thousand volts and to completely absorb a surge of large energy at the time of surge absorption. This causes a problem that, due to the residual voltage, a dynamic current (a current which flows into electronic equipment to be protected due to the presence of a residual voltage) arises in a circuit. Further, in the conventional devices, there is a problem that a switching voltage varies depending on specifications of the tube core.